Recently, there have been significant advances in the design of screw machines, such as described in U.S. Pat. Nos. 5,947,710 and 6,167,711, the disclosures of which are incorporated herein by reference. Based on these and other advances, “zero clearance” compressor screws have been produced, one of the main advantages of such compressors being that the screws may operate effectively and efficiently in the presence of minimal or no sealing and lubricating oil between the screw rotor profiles. However, it has proved difficult to achieve the associated high tolerances in the screw rotor profiles using techniques which are commercially viable.
It is known to coat metal components to provide selected surface characteristics, one of the most commonly used coating processes being electroplating. The majority of techniques used for electroplating are carried out under acidic conditions where the coatings formed are continuous and generally robust and thus provide effective anti-corrosion protection. By adding so-called “brighteners”, the formed coatings also have a high quality or “bright” finish. Examples of such techniques are described in European Patent Application No. 0100777 and U.S. Pat. Nos. 4,104,133, 6,071,631 and 5,283,131.
U.S. Pat. No. 5,435,898 relates to an alkaline electroplating process in which it is a specific object of this patent to form a ‘pit-free’ alloy deposit, obtained by using a quaternary ammonium polymer additive as a “brightener”.
It is among the objectives of at least one embodiment of the present invention to provide an economical method of coating a compressor component to provide the high tolerances necessary for successful operation of a zero clearance compressor screw.